The invention relates to a process for cooling a continuously cast ingot as it emerges from the mold during casting, and this by jetting coolant directly onto the peripheral part of the ingot.
When casting with direct cooling of the ingot, heat is extracted from the ingot as it emerges from the mold by jetting a coolant onto the ingot just below the mold. At the start of casting the coolant comes into contact only with the dummy base. The resultant indirect extraction of heat leads to a milder solidification of the liquid metal and to a flat ingot base. As the drop continues, the coolant strikes the ingot surface directly, which causes a sudden increase in the rate of heat extraction from the ingot. The stresses due to this thermal shock are greater than the yield strength of the ingot and lead to permanent deformation in the form of a convex doming of the ingot base and, on exceeding the tensile strength of the material, cause cracks in the ingot. To obtain an ingot with a flat base, therefore, the ingot must not be cooled too strongly at the start of the drop.
A process for reducing the cooling intensity at the start of casting is known whereby the coolant is pulsed as it is jetted.
Another process which is known makes use of gas dissolved in the coolant; when the coolant strikes the surface of the ingot, the gas forms an insulating film which reduces the rate of heat extraction.
These processes, however, also have disadvantages. The pulsating coolant produces vibrations which can have a deleterious effect on the structure forming in the ingot as it solidifies. Using coolant with gas dissolved in it on the other hand makes a complicated control facility necessary.
It is therefore an object of the invention to control the cooling in such a way that an essentially flat base is obtained. Also easy manipulation should be assured.